1. Field of the Invention
The present invention relates to arc-welding facilities and in particular to an arc-welding monitor.
The invention may be used in manual, mechanized and automatic arc welding, primarily with a consumable electrode in power engineering, construction of oil and gas pipe-lines, nuclear power engineering and shipbuilding.
2. Description of the Prior Art
A known weld quality monitor comprises welding current, voltage and speed sensors, a comparator for comparing each welding current, voltage and speed signal with a threshold value corresponding to optimal conditions, and a calculator utilizing welding current, voltage and speed signals to produce signals indicative of heat input, configuration of a weld and cooling rate.
During the welding operation, the afore-mentioned monitor monitors welding current, voltage and speed by comparing the monitored quantities with a reference value. An alarm is activated when a preselected variation in the measured and reference quantities occurs. The monitored quantities are also used to compute additional welding parameters including heat input, configuration of a weld and cooling rate, which are likewise compared to threshold values to monitor quality of a weld. The sensors used for measuring the welding parameters are selected so as to provide minimal interference with the welding process. For example, Hall effect transducers are used for current measurements, while unique opto-electronic noncontacting sensors are used for measuring welding speed (cf. U.S. Pat. No. 4,375,026).
In the known monitor the welding speed is monitored indirectly by a constant temperature difference over a constant weld length, which is not essentially speed monitoring since an indirect parameter indicative of a temperature difference depends not only on the welding speed but also on the welding current, voltage and other parameters. Moreover, any sporadic changes in current, voltage, speed and other welding parameters will not result in a variation of a temperature difference although quality of a weld will be adversely affected. Hence, welding speed variations from threshold values will not be accounted for, a disadvantage substantially decreasing accuracy in monitoring the given parameter.
From the aforesaid it follows that accuracy in monitoring general welding parameters determined by the calculator, more specifically, heat input, configuration of a weld and cooling rate will also be decreased due to its relation to the speed monitoring accuracy.
In the foregoing monitor no provision is made for monitoring such parameters as electrode slope, electrode feed rate disturbances, for example, in semiautomatic consumable-electrode gas-shielded arc welding, and supply-line voltage disturbances, for example, in manual and semiautomatic consumable-electrode arc welding, which substantially affect quality of a weld.
Furthermore, the known monitor may not be used to effect consecutive stage-by-stage welding monitoring due to the fact that selective activation of an alarm in response to a specific monitored quantity is impossible. The above limitation primarily concerns welding speed variations when alarm activation is generally ambiguous since speed signal variations are monitored indirectly by a change in a temperature difference although such variations may be caused by changes in other parameters excluding the speed, more specifically, by welding current and voltage changes.
Thus, in the known weld quality monitor accuracy and reliability of monitoring quality of a weld are fairly low, another disadvantage being low effectiveness in monitoring the welding process.
There is also known an apparatus for providing useful audio feedback to users of arc-welding equipment, wherein the user is provided with audible feedback signals which convey useful information relating to the output current and voltage of the welder (cf. U.S. Pat. No. 4,471,207).
The known apparatus comprises a weld power supply, a unit for generating a signal proportional to welding current, a unit for generating a signal proportional to welding voltage, said units being connected to said weld power supply, an audio-signal generator producing audio tones corresponding to welding parameters, a threshold element having its input connected to the output of the unit for generating a current-proportional signal and its output connected to the input of the audio-signal generator, a recorder connected to the outputs of the units for generating current- and voltage-proportional signals, and a welding operator's helmet with headphones at which audio signals arrive simultaneously with the recorder to enable audio monitoring of the arc-welding process.
The afore-mentioned apparatus operates in the following manner. An audio tone is generated and is frequency modulated by a signal which corresponds to welding voltage. The tone is amplitude modulated by a signal corresponding to welding current. Thus, the user is provided with a synthesized feedback signal having a voltage-proportional pitch and current-proportional volume. Additional modulation means are disclosed for introducing a current-proportional warble component to said tone.
In such an apparatus feedback signals obtained in monitoring are frequency and amplitude modulated, which makes it possible to evaluate quality of the welding process but prevents reliable and accurate quantitative monitoring of welding parameters (current and voltage).
The multiparametric welding process may not be monitored properly by using information relating to welding quality, which primarily concerns current and voltage changes. Although the welding process is appreciably affected by voltage and current changes, its stability ensuring a quality weld with desired characteristics and size over the entire length is attainable when a fairly large number of parameters are maintained within optimal limits. These are, for example, welding speed, electrode slope, as well as the previously mentioned welding current and voltage. Stabilization of the welding speed is required since its variation interferes with metallurgical reactions, which results in irregular input of heat, molten metal and additives, and also in isolation of metal from the air with gas or other shielding, a disadvantage causing changes in weld shape and depth. When speed variations are great, there may be undercuts and porosity in a weld due to unstable hydrodynamic conditions in a weldpool. Metal transfer in an arc and melting of base metal are noticeably affected by variations in electrode slope. By keeping it within predetermined limits, for example, in manual arc welding of groove joints, it is possible to uniformly deposit a layer of molten slag on molten metal in a bead and prevent hearth cinder from getting on unfused weld metal before reaching the arc. In mechanized gas-shielded arc welding, an undesirable change in electrode slope .theta. increases sputtering whereby input of heat, electrode and filler metal and other conditions will also change, a factor making occurrence of defects in a weld more probable. In the known apparatus, no account is made of changes in welding speed and electrode slope, which occur due to impaired welding conditions, for example, when the user is an inexperienced operator, a disadvantage preventing the monitoring of individual quantities or the set of parameters. As a result, reliability of monitoring the welding process is appreciably decreased.
Moreover, in the known apparatus use is made of only two interrelated parameters (welding current and voltage) with no account taken of other welding parameters, a feature preventing effective monitoring of the welding process due to the fact that the user is provided with feedback signals by changing audio frequency in the headphones in the event of any variations of individual parameters, for example, monitored welding voltage and current, including corresponding simultaneous changes in magnitude and sign of other parameters, for example, welding speed, which does not essentially affect conditions for obtaining a high quality weld. So, the welding operator receives superfluous audio feedback signals and may inadvertently impair quality of a weld. From the aforesaid it follows that the known apparatus does not permit consecutive stage-by-stage monitoring of the welding process, the first stage of which should involve monitoring of one predetermined quantity, for example, welding voltage or current, speed, or electrode slope, while at the second stage, best suited to satisfy the requirements for an actual quality weld, one or more parameters have to be monitored by comparing the measured values with reference data in different combinations thereof taking into account the interrelation between said parameters. Inasmuch as the known apparatus includes no such means, its accuracy in evaluating quality of the welding process is fairly low.
Moreover, the known device does not allow effective monitoring of the welding process for it utilizes the relationship between two welding parameters (current and voltage) by generating a tone having such variable characteristics as amplitude dependent on one parameter, for example, welding current and frequency dependent on the other parameter, for example, welding voltage. This disadvantage is attributed to the fact that it usually takes the welder a long time to adapt his ear for the frequency and amplitude of audio tones characteristic of quality welds under specific welding conditions. Adaptation for tone amplitudes takes more time since frequency characteristics of auditory ducts of an operator are of a more sensitive and permanent nature than their amplitude characteristics which are, to a large measure, dependent on physiological peculiarities of an individual.
So, recognition of a specific tone amplitude is more readily affected by such factors as audio welding characteristics, for example, noise arising from an arc, which may completely obscure the low-amplitude tone. Another factor to be taken into account is inadvertent displacement of headphones from auditory ducts of the welder, which substantially affects recognition of the tone amplitude, but has a less noticeable effect upon recognition of the tone frequency.
The welder's ability to recognize a specific (optimal) tone frequency indicative of a quality weld is impeded by utilization of different frequencies in the known apparatus to suit particular welding parameters determined by welding conditions. To obtain a quality weld in different welding conditions, said welding parameters should be suitably varied. Thus, the welding operator may not directly monitor quality of a weld in different welding conditions with the known apparatus wherein current values are set depending on other welding parameters.
Accuracy of monitoring the welding process and, consequently, its effectiveness are appreciably decreased due to a wide use of amplitude modulation of signals proportional to welding parameters and also of their frequency modulation without appropriately changing the parameters to obtain a quality weld in different welding conditions.
Moreover, qualitative monitoring of varying welding parameters prevents the known apparatus from determining to a fairly high accuracy the numerical values (i.e., setting signals) of said welding parameters corresponding to a quality weld and utilizing them for making the audio tone indicative of a quality weld.
In manual and mechanized arc welding, the operation of the known apparatus is adversely affected by disturbances of supply-line voltage. Such an effect leads to spontaneous variations of welding voltage and current from a predetermined value whereby spurious audio feedback signals will be heard in the welder's headphones, a factor interfering with normal monitoring.
Also, in mechanized gas-shielded arc welding, the operation of the afore-mentioned apparatus is adversely affected by electrode feed rate disturbances occurring primarily due to changes in the feeder drive speed. This results in spontaneous variations of welding current from a predetermined value whereby spurious audio feedback signals will be heard in the welder's headphones, a limitation impairing the monitoring process.